Ohmic contacts for a high-electron-mobility transistor

Abstract

Structures including an ohmic contact for a high-electron-mobility transistor and methods of forming such structures. The structure comprises a layer stack on a substrate and a device structure including an ohmic contact. The layer stack includes a plurality of semiconductor layers each comprising a compound semiconductor material. The ohmic contact includes a metal layer in a contacting relationship with a portion of at least one of the semiconductor layers of the layer stack and a region comprising oxygen atoms, and the metal layer is positioned between the region and the portion of the at least one of the semiconductor layers of the layer stack.

What is claimed is: 
     
       1. A structure comprising:
 a substrate; 
 a layer stack on the substrate, the layer stack including a plurality of semiconductor layers each comprising a compound semiconductor material; and 
 a device structure including a first ohmic contact, the first ohmic contact including a first metal layer in a contacting relationship with a first portion of at least one of the plurality of semiconductor layers of the layer stack and a first region comprising oxygen atoms, and the first metal layer positioned between the first region and the first portion of the at least one of the plurality of semiconductor layers of the layer stack. 
 
     
     
       2. The structure of  claim 1  wherein the first region further comprises aluminum atoms. 
     
     
       3. The structure of  claim 1  wherein the first metal layer comprises aluminum. 
     
     
       4. The structure of  claim 1  wherein the first metal layer exclusively comprises aluminum. 
     
     
       5. The structure of  claim 4  wherein the first metal layer is free of oxygen atoms. 
     
     
       6. The structure of  claim 1  wherein the first portion of the at least one of the plurality of semiconductor layers of the layer stack comprises gallium nitride. 
     
     
       7. The structure of  claim 1  wherein the first region is discontinuous. 
     
     
       8. The structure of  claim 1  wherein the first region is continuous. 
     
     
       9. The structure of  claim 1  wherein the first ohmic contact includes a second metal layer having a different composition from the first metal layer, and the first region is positioned between the first metal layer and the second metal layer. 
     
     
       10. The structure of  claim 1  wherein the device structure includes a second ohmic contact, the second ohmic contact includes a second metal layer in a contacting relationship with a second portion of the at least one of the plurality of semiconductor layers of the layer stack and a second region comprising oxygen atoms, and the second metal layer is positioned between the second region and the second portion of the at least one of the plurality of semiconductor layers of the layer stack. 
     
     
       11. The structure of  claim 10  wherein the device structure includes a gate laterally between the first ohmic contact and the second ohmic contact. 
     
     
       12. The structure of  claim 11  wherein the gate is positioned on the layer stack. 
     
     
       13. The structure of  claim 1  wherein the first metal layer fully separates the first region from the first portion of the at least one of the plurality of semiconductor layers of the layer stack. 
     
     
       14. A structure for forming an ohmic contact, the structure comprising:
 a substrate; 
 a first layer stack on the substrate, the first layer stack including a plurality of semiconductor layers each comprising a compound semiconductor material; and 
 a second layer stack on the first layer stack, the second layer stack including a first layer comprising silicon and oxygen adjacent to the first layer stack. 
 
     
     
       15. The structure of  claim 14  wherein the second layer stack includes a second layer comprising silicon between the first layer and the first layer stack. 
     
     
       16. The structure of  claim 15  wherein the second layer lacks oxygen atoms. 
     
     
       17. The structure of  claim 14  wherein the second layer stack includes a third layer on the first layer, a fourth layer on the third layer, and a fifth layer on the fourth layer, the third layer comprising a first metal, the fourth layer comprising a second metal, and the fifth layer comprising a third metal. 
     
     
       18. The structure of  claim 17  wherein the first metal is titanium, the second metal is aluminum, and the third metal is titanium. 
     
     
       19. A method comprising:
 forming a first layer stack on a substrate, wherein the first layer stack includes a plurality of semiconductor layers each comprising a compound semiconductor material; and 
 forming an ohmic contact of a device structure, wherein the ohmic contact includes a metal layer in a contacting relationship with a portion of at least one of the plurality of semiconductor layers of the first layer stack and a region comprising oxygen atoms, and the metal layer is positioned between the region and the portion of the at least one of the plurality of semiconductor layers of the first layer stack. 
 
     
     
       20. The method of  claim 19  wherein forming the ohmic contact of the device structure comprises:
 forming a first layer comprising silicon and a second layer comprising silicon dioxide on the first layer stack; 
 forming a second layer stack including a plurality of metal layers on the first layer and the second layer; and 
 annealing the first layer, the second layer, and the plurality of metal layers to form the ohmic contact.